(m). Global Surface Temperature Distribution

If the Earth was a homogeneous body without
the present land/ocean distribution, its temperature
distribution would be strictly latitudinal (Figure
7m-1). However, the Earth is more complex than this
being composed of a mosaic of land and water. This mosaic
causes latitudinal zonation of temperature to be disrupted
spatially.

Figure
7m-1: Simple
latitudinal zonation of temperature.

The following two factors are important
in influencing the distribution of temperature on the
Earth's surface:

The latitude of the location determines how much
solar radiation is received. Latitude influences
the angle of incidence and duration of daylength.

Surface properties - surfaces with high albedo absorb
less incident radiation. In general, land absorbs
less insolation that water because of its lighter
color. Also, even if two surfaces have the same albedo,
a surface's specific
heatdetermines the amount of heat energy
required for a specific rise in temperature per unit
mass. The specific heat of water is some five times
greater than that of rock and the land surface (see Table
7m-1 below). As a result, water requires the
input of large amounts of energy to cause a rise
in its temperature.

Table
7m-1: Specific
Heat of Various Substances.

Substance

Specific
Heat

Water

1.00

Air

0.24

Granite

0.19

Sand

0.19

Iron

0.11

Mainly because of specific
heat, land surfaces behave quite differently
from water surfaces. In general, the surface of any
extensive deep body of water heats more slowly and
cools more slowly than the surface of a large land
body. Other factors influencing the way land and
water surfaces heat and cool include:

Solar radiation warms an extensive layer in water,
on land just the immediate surface is heated.

The following images illustrate the Earth's
temperature distribution patterns for an average January
and July based on 39 years of data (Figures 7m-2 and 7m-3).
Note that the spatial variations of temperature on these
figures is mostly latitudinal. However, the horizontal
banding of isotherms is
somewhat upset by the fact that water heats up more slowly
in the summer and cools down more slowly in the winter
when compared to land surfaces. During January, much
of the terrestrial areas of the Northern Hemisphere are
below freezing (Figure 7m-2). Some notable Northern
Hemisphere cold-spots include the area around Baffin
Island Canada, Greenland, Siberia, and the Plateau of
Tibet. Temperatures over oceans tend to be hotter because
of the water's ability to hold heat energy.

In the Southern Hemisphere,
temperatures over the major landmasses are generally
greater than
20° Celsius with localized hot-spots in west-central
Australia, the Kalahari Desert in Africa, and the plains
of Bolivia, Paraguay, and Argentina (Figure 7m-2).
Subtropical oceans are often warmer than landmass areas
near the equator. At this latitude, land areas receive
less incoming solar radiation because of the daily convective development
of cumulus and cumulonimbus clouds.
In the mid-latitudes, oceans are often cooler than landmass
areas at similar latitudes. Terrestrial areas are warmer
because of the rapid heating of land surfaces under frequently
clear skies. Antarctica remains cold and below zero degrees
Celsius due to the presence of permanent glacial ice
which reflects much of the solar radiation received back
to space.

Figure
7m-2: Mean
January air temperature for the Earth's surface,
1959-1997. (Source of Original Modified Image:Climate
Lab Section of the Environmental Change Research
Group, Department of Geography, University of Oregon - Global
Climate Animations).

In July, the Northern Hemisphere is experiencing
its summer season because the North Pole is now tilted
towards the Sun (Figure 7m-3). Some conspicuous
hot-spots include the south-central United States, Arizona
and northwest Mexico, northern Africa, the Middle East,
India, Pakistan, and Afghanistan. Temperatures over oceans
tend to be relatively cooler because of the land's ability
to heat quickly. Two terrestrial areas of cooler temperatures
include Greenland and the Plateau of Tibet. In these
regions, most of the incoming solar radiation is sent
back to space because of the presence of reflective ice
and snow.

In the Southern Hemisphere, temperatures
over the major landmasses are generally cooler than ocean
surfaces at the same latitude (Figure 7m-3). Antarctica
is bitterly cold because it is experiencing total darkness.
Note that Antarctica is much colder than the Arctic was
during its winter season (Figures 7m-2 and 7m-3).
The Arctic consists mainly of ocean. During the summer,
this surface is able to absorb considerable quantities
of sunlight which is then converted into heat energy.
The heat stored in the ocean is carried over into the
winter season. Antarctica has a surface composed primarily
of snow and ice. This surface absorbs only a small amount
of the solar radiation during the summer. So it never
really heats up. As a result, the amount of heat energy
stored into the winter season is minimal.

Figure
7m-3: Mean
July air temperature for the Earth's surface, 1959-1997.
(Source of Original Modified Image:Climate
Lab Section of the Environmental Change Research
Group, Department of Geography, University of Oregon - Global
Climate Animations).

Figure 7m-4 describes average annual
global temperature data for the Earth for
the period 1982-1994. The patterns of temperature
distribution on this figure are once again mostly
latitudinal. However, the latitudinal banding is
partially upset by the fact that water bodies are
generally warmer than land surfaces. The image also
shows the effect of altitude (e.g., Himalayas and
Andes mountains) and albedo (Greenland
and Antarctica) on surface air temperature.

Average Annual Global Temperature 1982-1994

Temperature Scale in Kelvin

Figure
7m-4: Average
annual temperatures for the Earth's surface (1982-94).